Re: [RFC PATCH v2 5/6] KVM: arm64: Add support for KVM_EXIT_HYPERCALL
From: Sean Christopherson <seanjc@google.com>
Date: 2023-02-13 16:02:39
Also in:
kvmarm
Subsystem:
kernel virtual machine (kvm), the rest · Maintainers:
Paolo Bonzini, Linus Torvalds
On Sat, Feb 11, 2023, Oliver Upton wrote:
Finally, we need a flag to let userspace know what conduit instruction was used (i.e. SMC vs. HVC). Redefine the remaining padding in kvm_run::hypercall to accomplish this. Let's all take a moment to admire the flowers and see how 'longmode' tied up a full u32 in the UAPI. Weep.
I don't think it has to, at least not for other architectures. No other arch currently supports KVM_EXIT_HYPERCALL, so breakage is extremely unlikely. E.g. we can likely get away with this, and then just have x86 add new flags at bit 32.
diff --git a/include/uapi/linux/kvm.h b/include/uapi/linux/kvm.h
index 55155e262646..7d3ad820d55c 100644
--- a/include/uapi/linux/kvm.h
+++ b/include/uapi/linux/kvm.h@@ -341,8 +341,14 @@ struct kvm_run { __u64 nr; __u64 args[6]; __u64 ret; - __u32 longmode; - __u32 pad; + union { + /* + * Long Mode, a.k.a. 64-bit mode, takes up the + * first 32 flags on x86 (historical sludge). + */ + __u32 longmode; + __u64 flags; + }; } hypercall; /* KVM_EXIT_TPR_ACCESS */ struct {
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